The structural and regulatory properties of purified cyclic AMP-dependent protein kinase will be investigated. The enzymes will be crystallized and X-ray crystallographic studies will be carried out in collaboration with a different laboratory. Primary structural studies will be carried out on the holoenzyme and its subunits. Kinetic studies will be directed toward the elucidation of the mechanism of the protein kinase reaction. Comparative studies will be carried out with protein kinases derived from tissue other than skeletal muscle. The regulation of protein kinase activity of metabolites other than cyclic AMP will be studied. Specificity measurements will be made with the end in view of elucidating the relative importance of the primary, secondary and tertiary structure of protein substrates in protein phosphorylation reactions. Known substrates of the enzymes, as well as synthetic peptides, will be used. The subunit structure of muscle and liver phosphorylase kinase, together with other physicochemical parameters, will be investigated. The mechanism of action of Ca2 ion as an activator of the muscle enzyme will be explored. The regulation of liver phosphorylase kinase by cyclic AMP will be characterized. The regulation of liver phosphorylase phosphatase will be studied.